Lactulose is well known as a growth factor for bifidobacterium, and its effectiveness in maintaining human health is well documented. Moreover, this effectiveness is not restricted to humans, but has also been demonstrated in animal feed, meaning its use is being investigated in a wide variety of fields.
The effectiveness of lactulose in humans has been reported, for example in “The many faces of lactulose: recent research trends in development and physiological effects” (Milk Science, Vol. 50, No. 2 (2001), pp. 39 to 47), which discloses information relating to the growth activity on bifidobacterium. Through this activity, lactulose provides a variety of effects, including improving the environment within the intestine, improving excretion, and accelerating defecation, meaning the positive effects on human health are well known.
In addition, the effectiveness of lactulose in the field of animal feed has also been reported in “Process for producing lactulose-containing powders for livestock feed” disclosed in Japanese Examined Patent Application, Second Publication No. S54-15829, and this application reports a number of effects for lactulose-containing powders, including weight gains in young pigs, and improved feed efficiency.
Furthermore, Japanese Unexamined Patent Application, First Publication No. H7-39318 discloses the effectiveness of lactulose as a feed for fish. This application discloses that feed comprising from 0.01 to 10% of one or more oligosaccharides selected from the group consisting of fructooligosaccharide, galactooligosaccharide, xylooligosaccharide, isomaltooligosaccharide, soybean oligosaccharide, gentiooligosaccharide, raffinose and lactulose promoted the growth of fish.
As described above, the effectiveness of lactulose is very apparent, and as its importance becomes more widely recognized, the number of fields in which lactulose is used continues to grow.
However, lactulose is difficult to crystallize or convert to powder form, and conventionally is usually used as an aqueous solution, although new powders, which improve the ease of use, are now beginning to be developed and used.
One example of a process for producing powdered lactulose is disclosed in Japanese Examined Patent Application, Second Publication No. S40-861, and involves producing a lactulose dried product by spray drying an aqueous solution containing a solid fraction comprising lactulose, lactose and other carbohydrates as required, wherein the maximum concentration of the solid fraction is from 45 to 50%, and the maximum lactulose content within the solid fraction is from 45 to 50%.
However, the lactulose-containing powder composition produced by this conventional process, although powdered, suffers from a number of handling problems at the point of use, including a high hygroscopicity, and absorption of moisture leading to adhesion to the container or solidification when used under high humidity environments such as during rainy weather. Furthermore, although a dried product with improved free-flow characteristics can be obtained by lowering the lactulose content within the solid fraction of the aqueous solution supplied to the spray drying process, this results in a reduction in the lactulose content within the product powder, meaning the product is economically less viable and therefore impractical.
As an alternative, Japanese Examined Patent Application, Second Publication No. S49-44332 (Japanese Patent (Granted) Publication No. 778,565) discloses a process for producing a powder with a high lactulose content of at least 55%, by spray drying a lactulose aqueous solution containing a protein as a drying assistant, in a quantity equivalent to at least 5% of the quantity of lactulose.
However, the lactulose-containing powder composition produced by this process also suffers from high hygroscopicity and poor stability with respect to high humidity levels.
On the other hand, Japanese Unexamined Patent Application, First Publication No. H5-43590 (Japanese Patent (Granted) Publication No. 2,848,721) discloses the production of a non-hygroscopic, high-purity crystalline lactulose by concentrating a lactulose syrup containing lactose and galactose and the like in addition to lactulose, cooling the resulting concentrated syrup, adding lactulose seed crystals and stirring to generate crystalline lactulose trihydrate, and then separating this lactulose trihydrate.
However, the purification and crystallization step in this production process for crystalline lactulose is complex, and if the processing of the mother liquor left after separation of the crystals is also considered, then the process is costly, resulting in an increase in the cost of the final product.
The present invention takes the above circumstances into consideration, with an object of providing a method for producing a lactulose-containing powder composition that enables the production, via a simple set of steps, of a lactulose-containing powder composition with a practical lactulose content and superior stability to humidity, as well as providing a lactulose-containing powder composition produced by such a process, and a feed additive that uses such a powder.